The caller doesn't interact with the location server directly. A
redirect or proxy server asks the location server (which may be
co-resident with the SIP server or not) for "advice". The location
server is just a logical abstraction to indicate where the SIP server
gets its information from. The protocol between SIP server and location
server is beyond the scope of SIP. Examples of location servers include
- finger;
- LDAP/X.500;
- whois, whois++;
- ph and other local directories;
- shared file systems with registration on login;
- local SQL databases reached through TCP.
Also, callers don't register with the location server.
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